Honeycomb-like porous carbon frameworks with ultrathin carbon shells and enlarged interlayer spacing as anode for sodium-ion storage

The development of high-performance carbon anodes for sodium-ion batteries (SIBs) remains a challenge due to the sluggish kinetics and large ionic size of Na⁺. Herein, a novel and facile self-templating strategy is reported to synthesize three-dimensional honeycomb-like porous carbon frameworks featuring synergistically ultrathin carbon shells, enlarged interlayer spacing, and a hierarchical porous architecture. Sodium citrate is served as the carbon source and the self-template simultaneously, which simplifies the synthesis and enables the formation of this unique multi-level structure. The hollow honeycomb-like scaffold provides ample space for electrolyte infiltration and Na⁺ storage, while the ultrathin carbon shells and expanded interlayer spacing shorten ion diffusion paths and facilitate rapid Na⁺ intercalation. Benefiting from these merits, the optimized material delivers outstanding electrochemical performance as an anode for SIBs, including high reversible capacity (305.4 mAh g^-1 after 750 cycles at 200 mA g^-1 with an ultralow decay rate of 0.005 % per cycle) and superior rate capability (207.1 mAh g^-1 at 2000 mA g^-1). Kinetic analyses and in situ characterizations collectively confirm accelerated Na⁺ diffusion kinetics and a predominant pseudocapacitive Na⁺ storage mechanism. This work provides a cost-effective design principle for advanced carbon anodes in energy storage applications.